(a) Each induction system duct upstream of the first stage of the
engine supercharger and of the auxiliary power unit compressor must have a
drain to prevent the hazardous accumulation of fuel and moisture in the
ground attitude. No drain may discharge where it might cause a fire
(b) Each duct must be strong enough to prevent induction system failure
from normal backfire conditions.
(c) Each duct connected to components between which relative motion
could exist must have means for flexibility.
(d) Each duct within any fire zone for which a fire-extinguishing
system is required must be at least --
(1) Fireproof, if it passes through any firewall; or
(2) Fire resistant, for other ducts, except that ducts for auxiliary
power units must be fireproof within the auxiliary power unit fire zone.
(e) Each auxiliary power unit induction system duct must be fireproof
for a sufficient distance upstream of the auxiliary power unit compartment
to prevent hot gas reverse flow from burning through auxiliary power unit
ducts and entering any other compartment or area of the rotorcraft in
which a hazard would be created resulting from the entry of hot gases. The
materials used to form the remainder of the induction system duct and
plenum chamber of the auxiliary power unit must be capable of resisting
the maximum heat conditions likely to occur.
(f) Each auxiliary power unit induction system duct must be constructed
of materials that will not absorb or trap hazardous quantities of
flammable fluids that could be ignited in the event of a surge or reverse
flow condition. (Secs. 313(a), 601, 603, 604, Federal Aviation Act
of 1958 (49 U.S.C. 1354(a), 1421, 1423, 1424), sec. 6(c), Dept. of
Transportation Act (49 U.S.C. 1655(c)))